While the utility of zeolite P in detergent formulations has been acknowledged, for example in European Patent Application 0384070 (Unilever), they must be manufactured by a commercially effective process in order to become available on the market place. Thus, while the properties of a material may make it a useful commercial commodity, its manufacture has to be optimised for large scale production.
The zeolite P class includes a series of synthetic zeolite phases which may be in cubic configuration (also termed B or P.sub.c) or tetragonal configuration (also termed P.sub.1) but is not limited to these forms. The structure and characteristics of the zeolite P class are given in "Zeolite Molecular Sieves" of Donald W Breck (published 1974 and 1984 by Robert E Krieger of Florida USA). The zeolite P class has the typical oxide formula: EQU M.sub.2/n O.multidot.Al.sub.2 O.sub.3 .multidot.1.80-5.00 SiO.sub.2 .multidot.5H.sub.2 O
The present invention provides a process for preparing crystalline P-zeolites having Si:Al ratios from 0.9 to 1.33, which are particularly effective as detergent builders, preferably ratios of 1.15:1 and below and more preferably 1.07:1 and below.
M is an n-valent cation which for this invention is an alkali-metal, that is lithium, potassium, sodium, caesium or rubidium with sodium and potassium being preferred and sodium being the cation normally used in commercial processes.
Thus sodium may be present as the major cation with another alkali metal present in a minor proportion to provide a specific benefit.
The process of the present invention allows the production of P-zeolite with the above defined ratios at economic yield. During the formation of the crystalline zeolite the reacted medium passes through a gel stage. A preferred embodiment of the invention is the production of P-zeolites at a silicon:aluminium molar ratio of 1.00.+-.0.05 from a synthesis gel with the same compositional ratio.
This feature results in the desired product and a filtrate liquor containing essentially only sodium hydroxide. This liquor can be recirculated, after optional concentration, e.g. by evaporation, to the preparation of the initial reactant solutions. Another advantage of producing P-zeolites from a synthesis gel with the same silicon:aluminium ratio is that all the sodium silicate and the sodium aluminate are used thus optimising the consumption of the starting material.
Moreover, for detergents applications there is a need for a product with high oil absorption.